Reinforced blade

ABSTRACT

A propeller blade comprises a root, a tip distal from the root, a trailing edge extending from the root to the tip, a trailing edge, e.g. foam, insert, a shell forming an outer surface of the propeller blade and a plurality of stitches of yarn extending through two parts of the shell adjacent the trailing edge, wherein the yarns do not extend through the trailing edge insert.

FOREIGN PRIORITY

This application claims priority to European Patent Application No.16306461.1 filed Nov. 8, 2016, the entire contents of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to reinforced propeller blades.

BACKGROUND

The efficiency of a propeller blade may be improved by decreasing theaerodynamic thickness and radius of the propeller blade at its trailingedge. However, reducing the thickness and radius of a propeller bladealso reduces the structural integrity of the blade. Propeller blades mayneed a high damage tolerance capacity in order to prevent foreign objectdamage (FOD) from bird impact, for example.

Propeller blades may include leading edge and trailing edge inserts tocreate the desired aerodynamic profile of the blade and a shellsurrounding the inserts to provide structural strength to the blade. Thethickness of the blade at the trailing edge is therefore limited by thethickness of the trailing edge insert and the shell.

SUMMARY

From a first aspect, this disclosure provides a propeller bladecomprising a root, a tip distal from the root, a trailing edge extendingfrom the root to the tip, a trailing edge, e.g. foam, insert, a shellforming an outer surface of the propeller blade and a plurality ofstitches of yarn extending through two parts of the shell, for exampletwo opposing parts of the shell, adjacent the trailing edge, wherein theyarns do not extend through the trailing edge insert.

The stitches of yarn may be formed from at least one yarn extendingthrough the parts of the shell at more than one point along the span ofthe blade.

The plurality of stitches may comprise a row of stitches extending alonga portion of the span of the blade from the tip thereof, for example,least two rows of stitches extending along a portion of the span of theblade.

The portion may extend along less than 70% of the span and more than 20%of the span of the blade.

The propeller blade may further comprise a laminate sheet of compositematerial extending from a core of the propeller blade towards thetrailing edge, wherein the stitches of yarn also extend through thelaminate sheet.

This disclosure also provides a method of manufacturing a propellerblade comprising arranging a lightweight e.g. foam, trailing edge insertadjacent a trailing edge of a structural spar, surrounding the insertand structural spar with a shell and threading a yarn through the shelladjacent the trailing edge such that the yarn extends through two partsof the shell, for example two opposing parts, but does not extendthrough the insert.

Threading may be performed before surrounding the insert and structuralspar with the shell.

The shell may include at least two layers surrounding the blade and theyarn may be threaded through two parts of each of said at least twolayers, the method further comprising cutting an outer layer of the atleast two layers after the threading.

The threading may be performed with a vibrating needle or by tufting.

The threading may include forming at least one row of stitches extendingalong a portion of the span of the blade from the tip thereof, theportion extending along less than 70% of the span and more than 20% ofthe span of the blade.

The method may further comprise bonding a laminate sheet to thestructural spar and threading the yarn through the laminate sheet.

The yarn may be formed from carbon, glass or Kevlar®.

BRIEF DESCRIPTION OF DRAWINGS

Some embodiments of the disclosure will now be described by way ofexample only and with reference to the accompanying drawings in which:

FIG. 1 shows a portion of a propeller blade according to an embodimentof the invention;

FIG. 2 shows a cross-sectional view of the propeller blade of FIG. 1taken through line A-A;

FIG. 3 shows the trailing edge of a propeller blade of the prior art;and

FIG. 4 shows the trailing edge of a propeller blade according to anembodiment of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, an exemplary propeller blade 10 isillustrated. The propeller blade 10 has a leading edge 30, a trailingedge 32 a root (not shown) and a tip 40. The blade 10 further includes astructural spar 22, a leading edge insert 24 and a trailing edge insert26.

The structural spar 22 includes a central structural member 21, a sparfoam material 19 surrounded by the central structural member 21 along atleast a portion of the length of the central structural member 21 and anouter structural member 23, surrounding central structural member 21 andthe spar foam 19 along the entire length of the spar 22. Although thedescribed embodiment includes a spar foam material 19 in a centralregion thereof, it will be appreciated that the disclosure is applicableto hollow spars having a hollow central region with little or no foammaterial therein and spars having no core at all.

The central structural member 21 may be formed from pre-impregnatedlaminate sheets (pre-pregs). The pre-pregs may be impregnated with resinor thermoplastic material. Pre-pregs may increase the stiffness of thefoam to facilitate braiding thereon, by reducing or preventing bendingor deflection of the foam. Pre-pregs may also help prevent infiltrationof resin into the foam material during construction of the spar. Thespar foam 19 is formed from PU (polyurethane) foam material, althoughother foam or lightweight materials may be used, such as honeycombmaterials or balsa. The outer structural member 23 may be in the form ofa braided layer, for example comprising carbon fibres, although otherstructural materials may be used. In embodiments, the outer structuralmember 23 comprises unidirectional plies of carbon fibres.

The leading edge and trailing edge inserts 24, 26 are positionedadjacent the leading edge and trailing edge of the spar 22 respectivelyand are surrounded by a shell 28, for example, a Kevlar® sock. Inalternative embodiments the shell 28 could be in the form of a glassfibre or carbon fibre shell.

The blade 10 includes stitches of yarn 62 along the trailing edge 32 ofthe blade 10. The trailing edge stitches 62 extend from the tip 40 ofthe blade 10 towards the root of the blade 10 along a portion 32 a ofthe trailing edge 32. Although the trailing edge stitches 62 of theembodiment extend over a portion 32 a that is about one third of thelength of the trailing edge 32, it will be appreciated that the stitchesmay extend over a greater or lesser extent of the trailing edge 32 asrequired.

As shown in FIG. 2, the trailing edge stitches 62 extend through pliesof the shell 28 only. That is, there is no foam material of the trailingedge insert 26 between the plies of the shell 28 through which thetrailing edge stitches 62 extend. The trailing edge stitches 62therefore act to clamp two opposing parts of the shell 28 together, awayfrom the foam insert 26 in order to allow a thickness of the blade 10 atthe trailing edge 32 that is equal to the twice the thickness of theshell material 28 only.

For illustrative purposes, FIG. 3 shows a detail view of the trailingedge of a propeller blade 10 according to a known design. The trailingedge of blade 10 includes a trailing edge insert 26 and a shell 28, suchas a Kevlar® sock, extending around the insert 26. It will beappreciated that the minimum thickness of the blade 10 of this design istherefore limited by the thickness of the insert 26 at its trailing edgeas well as the thickness of the shell material 28.

FIG. 4 shows a detail view of a trailing edge region of a propellerblade 10 according to a further embodiment. The trailing edge 32 furtherincludes a sheet 64 of pre-preg material. The sheet 64 may be formedfrom plies of carbon or glass fibre fabric impregnated with an epoxyresin or thermoplastic material. The sheet 64 may be a separate sheet 64bonded to the central structural member 21. The sheet 64 extends towardsthe trailing edge 32 of the blade 10 beyond the trailing edge insert 26without foam material or hollow space therein. The sheet 64 may extendalong part of or the whole of the span S of the spar 22. In theseembodiments, the sheet 64 may be formed in a similar manner as describedabove. For example, pre-pregs for forming the sheet may be placed in themould and kept in compression along the trailing edge such that they arebonded together and no foam is injected therebetween.

Shell material 28 extends around the sheet 64. In this embodiment afirst layer 28 a of shell material extends around the trailing edge ofthe sheet 64 to form the trailing edge 32 of the blade 10. Furtherlayers or plies 28 b are attached to the first layer 28 a on an outersurface thereof on either side of the sheet 64. The further layers 28 bdo not extend all the way to the trailing edge 32 of the blade 10;rather they are spaced therefrom to further reduce the thickness of theblade 10 at its trailing edge 32. The further layers 28 b could beformed by cutting the outer layers of the shell 28 after application tothe blade 10 or could be cut or separately formed prior to applicationto the blade 10.

In the embodiment of FIG. 4, the shell material 28 includes two, spacedapart rows of stitches 62 in two regions adjacent the trailing edge 32.The first row of stiches 62 a extends through the sheet 64 and the firstlayer of shell material 28 a only. The second row of stitches 62 bextends through the sheet 64, the first layer of shell material 28 a andthe further layers of shell material 28 b.

The shell 28 may be stitched prior to attachment or may be provided withadditional pre-preg plies positioned in the trailing edge 32 to draw outthe shell 28 and enable subsequent stitching of the trailing edge 32 insitu. Shell 28 and spar 22 are injected with resin and the blade 10 isthen cured. In this way, the leading edge and trailing edge foam inserts24, 26 are bonded to the shell 28 and the shell 28 is also bonded to thespar 22, in a single co-curing process.

In any of the embodiments described above, the stitches of yarns 62 maybe arranged such that a single yarn 62 extends through the shell 28 morethan once. For example, a single yarn 62 may extend through the shell 28three or more times over a portion or the entire span S of the blade 10.Such yarns 62 may be threaded through the blade 10 in any number of waysas known in the art. For example, the yarns 62 may be threaded throughthe blade 10 using a stitching machine or by tufting. Stitching could beperformed by various methods as known in the art including with orwithout knots. In embodiments, the stitching may be performed with avibrating needle. The vibration applied to the needle facilitatespuncturing of the shell 28 and/or sheet 64. Tufting may involveinserting the yarns 62 through the shell 28 using a needle that, afterinsertion, moves back along the same trajectory leaving a loop of theyarn 62 on the bottom of the structure. All of the above-describedthreading techniques may be performed automatically. For example,stitching may be performed by a robot having a stitching head and needlemounted thereto.

Each yarn 62 or portion of yarn 62 extending through the shell 28 may bespaced from an adjacent yarn 62 or portion of yarn 62 extending throughthe shell 28 by a uniform distance across the span of the blade 10. Forexample the yarns 62 might be spaced between 3 and 15 millimetres apart,for example 5 millimetres in the span S direction.

Each yarn 62 may be formed from a dry carbon, glass or Kevlar® dry fibrematerial and may include a plurality of filaments of dry fibre materialtwisted with or bonded with one another to form a yarn 62.

Stitches of yarn 62 in the trailing edge 32 of the blade 10 help reducethe thickness of the blade 10 in this region as described above. Theyarns 62 may also reduce the amount of shell 28 repair required as aresult of de-burring resin after curing the blade 10. For example, theyarns 62 may help hold the shell 28 together to prevent cutting of theshell 28 when the blade 10 is being de-burred.

The yarns 62 adjacent the trailing edge 32 help reduce the aerodynamicthickness of the blade's profile and thereby increase the efficiency ofthe blade 10. The yarns may further improve static and fatigueinter-laminar shear strengths (ILSS) of the composite blade 10 andimprove damage tolerance and FOD strength.

The invention claimed is:
 1. A propeller blade comprising: a root; atip, distal from the root; a trailing edge extending from the root tothe tip; a structural spar; a trailing edge insert arranged between thestructural spar and the trailing edge; a shell forming an outer surfaceof the propeller blade, wherein the shell is a glass fiber resin shellor a carbon fiber resin shell; and a plurality of stitches of yarnextending through two opposing parts of the shell adjacent the trailingedge, wherein the yarns do not extend through the trailing edge insert.2. The propeller blade of claim 1, wherein the stitches of yarn areformed from at least one yarn extending through the opposing parts ofthe shell at more than one point along the span (S) of the blade.
 3. Thepropeller blade of claim 1, comprising a row of stitches of yarnextending along a portion of the span (S) of the blade from the tipthereof.
 4. The propeller blade of claim 3, comprising at least two rowsof stitches of yarn extending along the portion of the span of theblade.
 5. The propeller blade of claim 3, wherein said portion extendsalong less than 70% of the span (S) from the tip and more than 20% ofthe span (S) of the blade from the tip.
 6. The propeller blade of claim1, further comprising a laminate sheet of composite material extendingfrom the structural spar of the propeller blade towards the trailingedge and extending between the opposing parts of the shell, wherein thestitches of yarn also extend through the laminate sheet.
 7. Thepropeller blade of claim 1, wherein the yarn is formed from carbon orglass.
 8. The propeller blade of claim 1, wherein the trailing edgeinsert is a foam insert.
 9. The propeller blade of claim 1, wherein thestructural spar comprises: a spar foam material; a central structuralmember surrounding the spar foam material; and an outer structuralmaterial surrounding the central structural member.
 10. The propeller ofclaim 9, wherein the central structural member comprises a laminatesheet of composite material and the outer structural material is in theform of a braided layer.
 11. A method of manufacturing a propeller bladecomprising: arranging a trailing edge insert adjacent a trailing edge ofa structural spar; surrounding the trailing edge insert and structuralspar with a shell such that the trailing edge insert is arranged betweenthe structural spar and a trailing edge of the propeller blade, whereinthe shell is a glass fiber resin shell or a carbon fiber resin shell;and threading a yarn through the shell adjacent the trailing edge of thepropeller blade such that the yarn extends through two opposing parts ofthe shell but does not extend through the trailing edge insert.
 12. Themethod of claim 11, wherein the threading is performed beforesurrounding the insert and structural spar with the shell.
 13. Themethod of claim 11, wherein the shell includes at least two layerssurrounding the blade and the yarn is threaded through two parts of eachof said at least two layers, the method further comprising cutting anouter layer of the at least two layers after the threading.
 14. Themethod of claim 11, wherein the threading is performed with a vibratingneedle.
 15. The method of claim 11, wherein the threading is performedby tufting.
 16. The method of claim 11, wherein the threading includesforming at least one row of stitches extending along a portion of thespan (S) of the blade from a tip thereof, the portion extending alongless than 70% of the span (S) from the tip and more than 20% of the span(S) of the blade from the tip.
 17. The method of claim 11, furthercomprising bonding a laminate sheet to the structural spar and threadingthe yarn through the laminate sheet.
 18. The method of claim 11, whereinthe yarn is formed from carbon or glass.
 19. The method of claim 11,wherein the trailing edge insert is a foam insert.